Urea transport in the proximal convoluted tubule (PCT) occurs through passive diffusion, driven by the concentration gradient. Here's how it happens: 1. Mechanism of Urea Reabsorption in the PCT: In the PCT, about 50% of filtered urea is passively reabsorbed. This occurs as a result of solvent drag: Sodium (Na⁺), water, and other solutes are actively reabsorbed first. The reabsorption of water concentrates urea in the tubular fluid, creating a concentration gradient. Urea then passively diffuses across the tubular epithelium into the interstitial space. 2. Transport Pathways: Paracellular Pathway: Urea moves through tight junctions between tubular cells. Transcellular Pathway: Although the PCT lacks specialized urea transporters, urea can diffuse through the plasma membrane of tubular cells. 3. Regulation: The reabsorption of urea in the PCT is not directly regulated but is indirectly influenced by the rate of water reabsorption (which is driven by Na⁺ reabsorption). 4. Clinical Note: If there’s a disruption in kidney function (e.g., reduced glomerular filtration rate), urea can accumulate in the blood, leading to uremia.
Urea transport in the proximal convoluted tubule (PCT) occurs through passive diffusion, driven by the concentration gradient. Here's how it happens:
1. Mechanism of Urea Reabsorption in the PCT:
In the PCT, about 50% of filtered urea is passively reabsorbed.
This occurs as a result of solvent drag:
Sodium (Na⁺), water, and other solutes are actively reabsorbed first.
The reabsorption of water concentrates urea in the tubular fluid, creating a concentration gradient.
Urea then passively diffuses across the tubular epithelium into the interstitial space.
2. Transport Pathways:
Paracellular Pathway:
Urea moves through tight junctions between tubular cells.
Transcellular Pathway:
Although the PCT lacks specialized urea transporters, urea can diffuse through the plasma membrane of tubular cells.
3. Regulation:
The reabsorption of urea in the PCT is not directly regulated but is indirectly influenced by the rate of water reabsorption (which is driven by Na⁺ reabsorption).
4. Clinical Note:
If there’s a disruption in kidney function (e.g., reduced glomerular filtration rate), urea can accumulate in the blood, leading to uremia.